They can pay me with cash or check or PayPal or cc. I use Square to run the card in person right in front of them or to input the number over the phone. They can also go to my website and use the "make a payment" button. They can also pay by cc directly from the invoice I send them from my CRM. So, anyone that is concerned with giving out their info to me has other very easy ways to use a cc. I figure I am no more at risk handling their card than a clerk in the store or a cashier in the drive through or the person taking my order online.
More than likely if you do have issues it will be very sporadic. You might go weeks without anything going wrong then one day you have to unhook your quick disconnect on your airline to the pump once or twice which fixes any stalling issues every time then you might go weeks again with no issues. Like CAP said above, don't over think it. It will drive you nuts and usually won't happen anyway.
I suggest you keep everything as simple as possible, especially in the beginning. If and only IF you learn over time that you need to go with something more complicated do it then. I seriously doubt that going to the trouble of running your air line through the buffer tank is even worth considering at this point.
The choice between sizes doesn't have to just either/or. You can have more than one hose size if you want. I will guarantee you two things about the 3/4" hose-it will spray farther when you need it and it's major overkill 99.9% of the time when you don't. I totally agree about using the extra distance of the bigger hose when you need it for safety reasons to keep you off the roof but dragging it around to do a simple house wash or easy roof will get old in a hurry. The 5/8" hose with a 1" pump and a big ac will reach 99.9% of the roofs I do and I do mostly tall steep roofs. I get an easy 75' of distance horizontally. The key is keeping the other restrictions to a minimum. Eliminate unnecessary 3 way ball valves, avoid a trigger gun and use a 3/4" ball valve pvc pipe setup instead, don't use a hose reel unless the manifold is at least as big as your hose, unspool all of your hose and make sure it has no sharp turns in it, etc. and experiment with spray tips. Most importantly to max distance use the shortest length of hose you can! Any setup will spray farther with 75' of hose versus 300'. I use 3 sections of 5/8" hoses approximately 75' each with no hose reel and I camlock them together as needed. I keep an eye on the camlocks and have had zero issues with them coming apart, leaking etc. Just be careful when dragging hose around by relieving the strain on the joint by grabbing behind it same as you should do for the spray wand.
I have been using Slo Mo for the last few jobs and the stuff is AWESOME! It's crazy concentrated so it only takes a few ounces to do an entire roof. It also seems to clean extremely well and rinses easily. Try it you'll like it! I will definitely buy it again and nothing else.
They will call you and say that people in your area are looking for roof cleaners and that is probably true. What they don't tell you is that they are only IMPLYING these people are looking on Homeadvisor. They make it all sound really good, too. I guess it gets easy to make it sound good when it's all you do all day if you remember which lines people tend to fall for and use them. Leads, SEO, first page of Google, blah, blah, blah.
1" air pump is a good option. However, if you buy a used aodd pump for any roof cleaning operation be prepared to be disappointed. Chances are very good the pump will be 10 years + old and parts may or may not be even be available. Be prepared to have the used pump crap out in a year or less and then having to try to learn how to repair it IF you can find the parts and it's NOT easy to repair the air end if you've never done it. Time is money and spending an entire day or more working a pump doesn't cut it. Save yourself a lot of headaches and just buy new. It may cost you more up front but having a crapped out used pump AND a brand new one isn't cheap either!
The Eaton is a fine air compressor I am sure, but I know big HF ac is a beast because I have one and it will give you all the air you need. If you can afford the size and weight, the bigger air tank and smaller price tag for the HF make it a good choice, IMO.
No offense, but the "expensive, shiny" trap didn't stop with the system you greatly over paid for. I just looked at the surfactant you are using. $6.50 of that for every 50 gallon batch? That is a little steep, to say the least!
It will work for sure on siding and not at all on roofs. You may have to let it dwell for a few minutes before rinsing and may have to reapply a few times if really bad, but in most cases one application will be enough. I greatly prefer using my dedicated pump to clean siding over downstreaming with a pw but both have their advantages. The pw only requires the one hose which is nice, but I can apply the mix quicker with my dedicated pump, shoot much higher, use a stronger mix and rinse in a fraction of the time.